function Person(a) {
  this.a = a;
}

function newObj(fn, ...arg) {
  const obj = Object.create(fn.prototype); // 把对象的__proto__ 指向构造函数的 prototype
  obj._fn = fn;
  obj._fn(...arg);
  delete obj._fn;
  return obj;
}

const obj = newObj(Person, 5);

console.log(obj);
